Many "counter-current" ion exchange methods have already been described. In such methods, the fixation of the ions on the ion exchanger granular materials and the regeneration of the granular materials are carried out by means of liquids flowing counter-current. Some operate from bottom to top for the fixation cycles and from top to bottom for the regeneration cycles. The disadvantage of such methods is that they support with difficulty the inadvertent stoppages and restarts, the layers of granular material falling back with more or less rapidity and mixing together, which is the cause of poor quality of the treated liquid.
The methods operating from top to bottom for the fixation cycles and from bottom to top for the regeneration cycles avoid this disadvantage by maintaining the layers of granular materials in a compact state.
In these methods however, the impurities present in the liquid to be treated are retained in the granular material layer, interfering with its action and increasing the load loss, and therefore, such impurities have to be periodically removed by decompaction and washing. But the decompaction and washing operations disturb the granular material layer. This disturbance is very important in the methods operating from bottom to top for the fixation cycles since impurities are dispersed over the whole height of the granular material layer, which has to be cleaned in its totality.
In the methods operating from top to bottom for the fixation cycles, the impurities are retained almost totally in the upper portion of the granular material bed acting as a filter.
The method disclosed in French patent No. 2 443 283 avoids this disadvantage by a transfer, by means of a current of liquid circulating from top to bottom, of the upper portion of the granular material bed to an appendant receptacle provided for the decompaction and washing of the granular material. However this method requires an outer column for the washing of the granular material, implying a succession of relatively lengthy operations which preferably have to be carried out only at distant intervals of time.
The present invention remedies this disadvantage by making it possible to carry out the operations of decompaction and washing of the granular material in the same receptacle in which are carried out the fixation and regeneration operations.
When practicing the methods in which the liquid to be treated circulates from top to bottom, it has been established that the impurities contained in the liquid to be treated as well as the finer resin balls concentrate in the upper layer of the ion exchanger resin bed, whereby such impurities, independently of the resin bed size, penetrate hardly further than into a layer of about 30 cm in thickness.